After validation of an isotope delutions method for quantitaling forearm norepinephrine release and thus sympathetic neural activity in respose to standing and hypoglycemia, we will test the hypothesis that glycemic thresholds for sympathetic neural responses to hypoglycemia, like those for adrenomedullary and parasympathetic neural responses are elevated (lower plasma glucose concentrations required) following recent antecedent hypoglycemia in humans.